Synthesis and identifying the active site of Cu2Se@CoSe nano-composite for enhanced electrocatalytic oxygen evolution

The urgent demand for clean energy sources has led the oxygen evolution reaction (OER) became one of the most essential reaction due to its "rate-determining" nature for electrolysis of water. In this paper, a nano-composite of Cu₂Se@CoSe was synthesized using a colloidal method. This synthetic approach was capable for the synthesis of Cu₂Se, CoSe and Cu₂Se@CoSe. The nano-composite of Cu₂Se@CoSe exhibited electrocatalytic OER activity, with low overpotential of 251 mV at 10 mA cm⁻² and 320 mV at 100 mA cm⁻², and even beat the RuO₂ at high current density (i.e.> 80 mA cm⁻²). Long-term electrolysis test revealed the chemical and electrochemical stability over 20 h at high current density (150 mA cm⁻²). Furthermore, post-electrolysis experimental analyses indicated that CoOOH/Cu(OH)₂ on Cu₂Se@CoSe played an important role in OER electrocatalysis, and they were readily oxidized from Cu⁺ in Cu₂Se and Co²⁺ in CoSe before the onset potential of OH⁻ oxidation. The CoOOH/Cu(OH)₂ served as both catalytic material and protective layer of Cu₂Se@CoSe, thus leading to enhanced OER catalytic activity and stability. It is believed that Cu₂Se@CoSe can be a potential candidate for fabricating sustainable OER electrocatalytic electrode.